In a Long Term Evolution (LTE) system, seven TDD uplink/downlink configurations are defined for each Time Division Duplex (TDD) radio frame, particularly as depicted in Table 1, where D represents a downlink sub-frame, U represents an uplink sub-frame, and S represents a special sub-frame. The special sub-frame is composed of three components including a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS).
TABLE 1(Uplink/downlink configurations of TDD system)DownlinkUplink/to uplinkdownlinkswitchingSub-frame numberconfigurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
There are significantly improved system peak rates in a Long Term Evolution-Advanced (LTE-A) system as compared with the LTE system, and a bandwidth available to a User Equipment (UE) needs to be extended by aggregating together a plurality of consecutive or inconsecutive carriers to serve the UE concurrently, particularly as illustrated in FIG. 1. These carriers aggregated together are referred to as component carriers. Each cell can be a component carrier.
In the Rel-10 system, the same TDD uplink/downlink configuration applies to a plurality of component carriers aggregated for the UE, and the UE is notified of the configuration via a System Information Block-1 (SIB-1), so the configuration can also be referred simply to as an SIB-1 TDD uplink/downlink configuration. In The Rel-11 and releases subsequent thereto, a Carrier Aggregation (CA)-enabled UE can share or access an adjacent band with another system. As illustrated in FIG. 2, for example, three carriers are aggregated for the UE: the carrier 1 and the carrier 2 are located in the band 1 and the carrier 3 is located in the band 2. In order to avoid uplink/downlink cross interference between the adjacent TDD systems, the same TDD uplink/downlink configuration as the 3G/LTE TDD band A shall apply to the carrier 1 and the carrier 2, and the same TDD uplink/downlink configuration as the 3G/LTE TDD band B shall apply to the carrier 3. When there are different TDD uplink/downlink configurations in the band A and the band B, the TDD uplink/downlink configuration of the carriers 1 and 2 is different from the TDD uplink/downlink configuration of the carrier 3, where carriers 1, 2 and 3 are aggregated for the UE.
When component carriers with different TDD uplink/downlink configurations are aggregated for the UE, in order to enable the different component carriers to normally obtain scheduling information and perform an Acknowledgement/Non-Acknowledgement (ACK/NACK) feedback, it is necessary to define for each carrier a downlink reference TDD uplink/downlink configuration for determining downlink Hybrid Automatic Repeat reQuest (HARQ) timing (simply DL HARQ timing) of the carrier, and an uplink reference TDD uplink/downlink configuration for determining uplink scheduling and HARQ timing (simply UL scheduling/HARQ timing) of the carrier, respectively, where the so-called DL HARQ timing refers to relationship between a downlink sub-frame of a carrier and an uplink sub-frame in which ACK/NACK information of the downlink sub-frame is transmitted, and the so-called UL scheduling/HARQ timing refers to relationship between an uplink sub-frame of a carrier and a downlink sub-frame in which scheduling information of the uplink sub-frame is transmitted, and relationship between an uplink sub-frame of a carrier and a downlink sub-frame in which ACK/NACK information of the uplink sub-frame is transmitted.
As currently specified, both the downlink reference TDD uplink/downlink configuration and the uplink reference TDD uplink/downlink configuration of a Primary Component Carrier (PCC) are the SIB-1 TDD uplink/downlink configuration of the PCC, and the downlink reference TDD uplink/downlink configuration of a Secondary Component Carrier (SCC) is dependent upon particular configurations of the SCC and the PCC, which may be the SIB1 TDD uplink/downlink configuration of the PCC or the SIB1 TDD uplink/downlink configuration of the SCC or may be another TDD uplink/downlink configuration, particularly as specified in the standard; and the uplink reference TDD uplink/downlink configuration of the SCC is the SIB-1 TDD uplink/downlink configuration of the SCC in self-carrier scheduling, and may be the SIB-1 TDD uplink/downlink configuration of the SCC or the SIB-1 TDD uplink/downlink configuration of the scheduling CC in cross-carrier scheduling, particularly as specified in the standard.
In the LTE system, a Physical Downlink Control Channel (PDCCH) is primarily configured to transmit scheduling information and power control commands of uplink and downlink traffic. Different Downlink Control Information (DCI) formats are defined for different applications and different carried information contents of the scheduling information. The DCI formats 1/1A/1B/1C/1D/2/2A/2B/2C can be applicable to a PDCCH carried with downlink scheduling information, the DCI formats 0/4 can be applicable to a PDCCH carried with uplink scheduling information, and the DCI formats 3/3A can be applicable to a PDCCH carried with a group of uplink power control command, where the DCI formats 1C/3/3A can only be transmitted in Common Search Space (CSS), the DCI formats 0/1A can be transmitted in CSS and UE-specific Search Space (USS), and the remaining DCI formats can only be transmitted in USS.
The UE needs to detect a PDCCH over two sets of resources, i.e., in CSS and USS. The CSS only present in a primary cell is shared by all of UEs in the cell and primarily used to transmit scheduling signaling of common information, so the size of DCI (i.e., the number of bits in the DCI) transmitted in the CSS must be uniform for all UEs. The USS present on a scheduling carrier of the UE is used to transmit scheduling signaling of UE-specific data, and sizes of DCI of different UEs may be different. Detection of a PDCCH by a UE is blind detection, that is, the UE attempts to identify a correct PDCCH at different Control Channel Element (CCE) aggregation levels and different sizes of DCI. Generally the different DCI formats differ in size with different particular information carried therein. In order to reduce the number of times that the UE performs blind detection of a PDCCH, bit padding has been introduced to satisfy the following conditions:                a. Any DCI format includes a different number of bits from predefined ambiguous numbers of bits {12, 14, 16, 20, 24, 26, 32, 40, 44, 56} so that the UE will not detect a plurality of PDCCH starting locations;        b. There is a uniform size of the DCI formats 0/1A/3/3A in the same search space, so the UE can detect in the same search space the DCI formats 0/1A/3/3A at only one size of DCI and distinguish between the DCI formats 0/1A, the DCI format 3 and the DCI format 3A by different Cell-Radio Network Temporary Identifiers (C-RNTIs) for scrambling Cyclic Redundancy Check (CRC) of a PDCCH and further distinguish between the DCI format 0 and the DCI format 1A by a 1-bit identifier in the DCI formats 0/1A;        c. When the CRC of a PDCCH is not scrambled by a C-RNTI, the size of the DCI format 1 is the same as the size of the DCI formats 0/1A; and        d. When the CRC of a PDCCH is scrambled by a C-RNTI, there are a different size of the DCI formats 1/1B/1D from that of the DCI formats 0/1A and a different size of the DCI format 4 from that of the DCI formats 1/2/2A/2B/2C, for scheduling the same carrier, transmitted in the same USS, so that the UE distinguishes between the different DCI formats by their sizes of DCI;        
In the LTE-A Rel-10 system, only one of 2-bit Uplink (UL) index field and 2-bit Downlink Assignment Index (DAI) field is present in the DCI formats 0/4 at a time, and the UL index is only present when the SIB-1 TDD uplink/downlink configuration of the UE is configuration 0, to indicate whether a plurality of UL sub-frames are scheduled concurrently in a DL sub-frame (i.e., uplink multi-subframe scheduling) when there are more TDD UL sub-frames than DL sub-frames, so that each UL sub-frame can be provided with scheduling information; and the DAI is only present when the SIB-1 TDD uplink/downlink configurations of the UE belongs to configuration 1 to 6, so that when ACK/NACK information corresponding to a plurality of downlink sub-frames is to be fed back concurrently in an uplink sub-frame in the TDD system (that is, a value of M of the carrier is larger than 1, where M represents the number of elements, i.e., the number of downlink sub-frames including special sub-frames for which ACK/NACK needs to be fed back, in a set of downlink indexes associated with an uplink sub-frame, determined from the SIB-1 TDD uplink/downlink configuration configured for the UE), the number of ACK/NACK feedback bits corresponding to each carrier is determined from a value indicated in the DAI field to thereby reduce a resource overhead of ACK/NACK over a PUSCH while avoiding inconsistent understanding of an eNB and the UE about the number of ACK/NACK feedback bits transmitted over the PUSCH.
When carriers with different TDD uplink/downlink configurations are aggregated, different reference TDD uplink/downlink configurations may be used for DL HARQ timing and UL scheduling/HARQ timing of different component carriers, and different reference TDD uplink/downlink configurations may also be used for DL HARQ timing and UL scheduling/HARQ timing on the same component carrier.
In the prior art, the method in the Rel-10 of judging from an SIB-1 TDD uplink/downlink configuration of a UE whether a DCI format is to contain the UL index or the DAI can not accommodate the demand above, and may even cause the presence of both the UL index and the DAI in the DCI format, for example, when two carriers configured with the SIB-1 TDD uplink/downlink configurations 0 and 1 are aggregated for the UE, a change in size of a DCI format transmitted in a CSS may impose an influence upon normal transmission of cell common information. Thus the method in the Rel-10 of judging whether a DCI format is to contain the UL index or the DAI will not be applicable to the inter-band carrier aggregation system any more, and there has been absent so far a specific method of judging whether a DCI format is to contain the UL index and/or the DAI for a UE with inter-band carrier aggregation.